Inductively triggered breakerless ignition system with variable magnetic shunt



A r-i121, 1970 BQBURSQN 3, 8, 6

RIGGERED B INDUCTIVELY T REAKE'RLESS IGNITION SYSTEM WITH VARIABLE MAGNET SHUNT Filed Sept. 9. 1968 INVENTOR. BOB O. BURSON WI ATTORNEYS United States Patent O US. Cl. 317-81 7 Claims ABSTRACT OF THE DISCLOSURE An ignition system for a spark ignited engine includes a silicon controlled rectifier for controlling the firing of the associated spark plug. The silicon controlled rectifier is triggered by signals provided by a triggering magnet and coil assembly mounted adjacent a rotating part of the engine including an iron pin or other pole means for varying the reluctance of the magnetic circuit through the triggering coil as the rotating part is rotated to induce a triggering voltage signal in the coil. A means is also provided for establishing a shunt circuit of adjustable reluctance for the flux produced by the magnet to permit the system to be easily calibrated to fire at a desired given point or angular position of said rotating part at a given speed thereof, thereby compensating for variations from unit to unit in the parts of the system.

BACKGROUND OF THE INVENTION This invention relates to breakerless ignition systems utilizing inductively triggered components for controlling the timing of the firing, and deals more particularly with such systems wherein a variable reluctance magnetic shunt circuit is provided in combination with the main magnetic circuit of the triggering system for varying the timing of the triggering.

In breakerless ignition systems, it is customary to use a. transistor, silicon controlled rectifier or other triggered electronic switch device for controlling the timing of the firing of the associated spark plug or other spark gap ignition device. It is also customary to provide triggering signals for such an electronic switch device through the use of a magnet and coil assembly located near a rotating part of the associated engine and having a triggering signal induced therein by an iron pin or other pole forming means carried by the rotating part. In producing such ignition systems in quantity, however, it is found that the components may vary widely in their individual characteristics and, therefore, the finished systems may vary considerably as to the point at which they cause firing to occur at a given speed of the rotating part. The greatest variation is usually found to occur in the characteristics of the electronic switching components. For example, if silicon controlled rectifiers are used as the electronic switch devices, it is found that they may vary as much as 300 to 400 percent in their triggering characteristics so that one may be triggered bya relatively low voltage and low current triggering signal and another may require a relatively high voltage and high current triggering signal to be triggered. In the past, this problem has been overcome by providing an adjustment in the electrical portion of the triggering circuit and has usually involved the use of a resistor in parallel or in series with the triggering or gate terminal of the switch device in order to suit the triggering to the particular voltage existing across the triggering coil winding at the instant firing is desired. This form of adjustment or calibration is relatively time consuming and expensive insofar as each system has to be tested individually and matched with a properly valued resistor, and care has to be exercised that the selected resistor is thereafter kept with the system. This form of adjustment or calibration also has a disadvantage the fact that it requires all of the systems to be calibrated to meet the performance of the otherwise least acceptable or worst system.

The variable magnetic shunt of this invention provides an adjustment or calibration which is very simple to make and considerably less expensive than adjustments made to the electrical portion of the triggering circuit.

SUMMARY OF THE INVENTION The invention resides in a breakerless ignition system for a spark ignited engine including a triggered electronic switch device for controlling the timing of the firing of the spark plug or other spark gap ignition device. Triggering signals are provided by a magnet and coil assembly located adjacent a rotating part of the engine which carries an iron pin or other pole forming device for varying the reluctance of the flux circuit through the coil as the rotating part rotates. An additional means is provided for establishing a second shunt circuit for magnetic flux in parallel with the circuit passing through the coil. This shunt circuit includes an air gap or area of reduced cross-section and a means for varying the reluctance of the air gap or area of reduced cross-section to thereby vary the reluctance of the shunt circuit and the amount of flux diverted from the circuit through the coil. Therefore, by varying the amount of flux supplied to the coil the point at which the voltage induced in the triggering coil reaches the triggering level is readily controlled.

BRIEF DESCRIPTION OF THE DRAWING FIG. 1 is a view showing the physical components of an ignition system embodying this invention, the rotating part of the engine being shown fragmentarily and in section.

FIG. 2 is a sectional view taken on the line 22 of FIG. 1.

FIG. 3 is a sectional View taken on the line 3-3 of FIG. 1.

FIG. 4 is a schematic wiring diagram of an ignition system utilizing the physical components of FIG. 1.

FIG. 5 is a sectional view generally similar to FIG. 3 but showing a different means for providing the magnetic shunt circuit.

FIG. 6 is a view of another triggering magnet, coil and shunt circuit forming means for use in an ignition system comprising another embodiment of this invention.

FIG. 7 is a view taken on the line 7-7 of FIG. 6.

DESCRIPTION OF THE PREFERRED EMBODIMENTS Turning to the drawings and first considering FIGS. 1 to 4, these figures relate to one form of breakerless ignition system embodying this invention. The physical components of the system are shown in FIGS. 1, 2, and 3, and the electrical circuit is shown in FIG. 4. In FIGS. 1, 2, and 3 the part 20 is the part, such as the rim of a flywheel, which is rotated in synchronism with the operation of the associated engine, the part being rotated in the clockwise direction as indicated by the arrow of FIG. 1. In the rim 20 is a main magnet assembly consisting of a permanent magnet 22 andtwo circumferentially extending and circumferentially spaced pole pieces 24, 24 providing inwardly directed pole faces 26, 26 which cooperate with a stationary pole piece 28 and energizing coil 30, located inside of the rim, for inducing in the coil 30' the voltage used for producing the spark at the associated spark plug or other spark gap ignition device as hereinafter described.

The rim 20 is made of a non-magnetic material, such as aluminum, and includes a means, such as an outwardly extending iron or steel pin 32, fixed thereto for varying the reluctance of the flux circuit passing through the coil 34 of a triggering magnet and coil assembly, indicated generally at 36, located adjacent the rim. The magnet and coil assembly 36, in addition to the triggering coil 34, includes an annular permanent magnet 38 charged so as to have opposite magnetic poles at its opposite end faces 40 and 42. Engaging the lower end face 42 is a ferromagnetic element in the form of a steel plate 44 which extends radially outwardly beyond one side of the magnet 38. Likewise, engaging the top end face 40 of the magnet 38 is another ferro-magnetic element in the form of a steel plate 46 which includes a portion extending outwardly of the magnet in alignment with the outwardly extending portion of the bottom plate 44. The upper plate 46 is also bent as shown to form an arm 48 for use in mounting the assembly 36 to the fixed structure of the engine. The coil 34 is received on a ferromagnetic core or plug 50 and the two plates 44 and 46, the magnet 38, and the coil 34 are held in assembly by a screw 52 of 'brass or other non-magnetic material passing through the plates and the magnet and threaded into the coil core 50.

As mentioned, the triggering magnet and coil assembly 36 is located adjacent the rotating part or rim 20. A flux circuit, comprised mainly of leakage flux, indicated by the broken lines 54, 54, passes between the opposite end faces of the magnet 38 and through the coil 34. As the iron pin 32 on the rim 20 passes the end face of the coil core 50, as shown in FIG. 1, it decreases the reluctance of this flux circuit through the coil 34 and induces a voltage in the coil used to trigger the electronic switch device of the associated electrical circuit of the system.

The two portions of the plates 44 and 46 which extend outwardly of the magnet 38 comprise part of a magnetic shunt circuit for adjustably controlling the value of the maximum voltage induced in the coil 34. The remainder of this shunt circuit is provided by a ferromagnetic screw 58 threadably received in the plate 46 and extending toward the plate 44. The end of the screw 58 therefore defines an air gap 60 with the plate 44 which may be varied in size by turning the screw in one direction or another to vary the reluctance of the shunt circuit. The shunt circuit serves to divert some of the magnetic flux produced by the magnet 38 away from the circuit passing through the coil 34. Therefore, by changing the reluctance of this shunt circuit, as by turning the screw 58, the amount of flux passing through the coil 38 may be varied to control the voltage induced in the coil so that at a given speed of the part 20 the exact voltage required to trigger the associated electronic switch device is produced at a desired angular position of the part.

The electrical portion of the ignition system used with the magnet and coil assembly 36 may vary widely, but in the illustrated case, as shown in FIG. 4, this system is a condenser discharge system. Referring to FIG. 4, the spark plug is indicated at 62 and, as mentioned, the energy for forming the spark at the plug is provided by the voltage induced in the energizing coil 30. A condenser 64 is connected across the coil 30 and also across the primary winding 67 of a step-up transformer 68. A diode 70 is connected in parallel with the coil 30 and rectifies the power supplied to the condenser 64 so that only positive pulses are transmitted thereto. Another rectifier 72 is .connected in series with the coil 30 and prevents the charge on the condenser 64 from returning to the coil 30 during the negative portion of each cycle. Between the positive side of the condenser 64 and the adjacent end of the primary winding 67 of the transformer 68 is a silicon controlled rectifier 74 which serves as an electronic switch device for controlling the discharge of the condenser through the primary winding 67. That is, during the operation of the system the condenser 64 is first charged while the silicon controlled rectifier is in a nonconducting state and then the silicon controlled rectifier is thereafter triggered from its non-conducting state to a conducting state so that the condenser is suddenly discharged through the primary winding 67 to produce a surge of current through such winding which induces a high voltage in the secondary winding 76 to in turn produce a spark at the spark plug 62. i

The triggering of the silicon controlled rectifier 74 is controlled by the triggering coil 34 of the magnet and coil assembly 36 which is connected between the gate and cathode terminals of the silicon controlled rectifier. Therefore, when the triggering voltage induced in the triggering coil 34 reaches the triggering level of the silicon controlled rectifier 74, the latter is triggered to produce firing of the spark plug. The triggering characteristics of silicon controlled rectifiers are known to vary widely from unit to unit and, therefore, in accordance with this invention, after an ignition system, such as that shown in FIG. 4, is assembled, the timing of the firing of thespark plug 62 may be caused to occur at any desired point, for a given speed of the engine, despite such variation in the silicon controlled rectifier, by adjusting the screw 58 to vary the reluctance of the shunt circuit and to thereby match the voltage induced in the triggering winding to the particular silicon controlled rectifier used in the assembly.

The nature of the adjustably variable reluctance magnetic shunt circuit may vary widely without departing from the spirit of this invention. For example, FIG. 5 shows an alternative construction of the triggeringmagnet and coil assembly wherein the magnet 78, similar to the magnet 38 of FIGS. 1, 2 and 3, is annular in shape and charged so as to have opposite magnetic poles at its opposite end faces. One circular plate 80 of ferromagnetic material engages the upper end face of the magnet and another circular plate 82 of ferromagnetic material engages the bottom end face of the magnet. The triggering coil 84 is wound on a ferromagnetic core 86 which, at its upper end, includes a stud portion 88 which passes through the plate and is peened to fix the coil 84 and its core 86 to the plate 82. The stud portion of the core is located Within the center opening of the magnet 78. Also extending partially through this opening is a, ferromagnetic screw 90 threadedly received by the upper plate 80. The screw 90 in conjunction with the stud portion 88 of the core 86 forms a magnetic shunt circuit for the magnet 78 and includes an air gap 92 which may be varied to vary the reluctance of such shunt circuit by turning the screw 90 in one direction or another. A suitable means, such as plastic housing (not shown) surrounding the magnet and coil and exposing only the lower face of the core 86 and the head of the screw 90 may be used to hold the various parts in their assembled relation.

FIGS. 6 and 7 show another form of triggering magnet and coil assembly made in accordance with this invention. Referring to these figures, the triggering magnet and coil assembly is indicated generally at 96 and is shown positioned inside of the rim 20 and arranged so that the reluctance of the flux circuit through the triggering coil is varied by the pole pieces 24, 24. This eliminates the need for a separate pole means, such as the pin 32 of FIG. 1, for varying the reluctance of the circuit through the triggering coil. The magnet of the assembly is shown at 98, and associated with it are two similar ferromagnetic pole pieces 100, 100 each of which engages a respective face or pole of the magnet. Each pole piece 100 includes a leg 104 which extends inwardly toward the inner face of the rim 20 for cooperation with the pole pieces 24, 24. The triggering coil 108 is received on one leg 104. Therefore, as the leading pole piece 24 is brought into alignment with the magnet and coil assembly 96, by rotation of the rim 20, the reluctance of the flux path through the winding 108 is suddenly decreased so as to induce a triggering voltage therein.

A magnetic shunt circuit for the magnet 98 is provided by forming each pole piece 100 so as to have a second leg portion 110, extending away from the magnet 98 and beyond the end edge 109 of the rim 20. Each leg 110 terminates in a face 111 serving as a pole face for the magnet 98. Associated with the two pole faces 111, 111 so provided is a movable plate 112 pivotally connected to a fixed part 114 of the engine for movement about a pivot axis 116 across the faces 111, 111. In FIG. 6, the solid lines show the plate 112 in one position of its movement and the broken lines show it in another position. From this, it will be noted that the plate 112 is of such a shape that in different ones of its positions it overlaps different areas of the pole faces 111, 111. The magnetic shunt circuit passes through the legs 110, 110 and the plate 112 and the minimum cross-sectional area of such flux circuit occurs at the point where the plate overlaps one of the pole faces 111, 111. This in turn controls the reluctance of the shunt circuit, and by shifting the position of the plate 112 to vary this area of overlap the reluctance of the shunt circuit may be likewise varied to vary the amount of flux circuit passing through the triggering winding 108 and to thereby vary the value of the triggering voltage induced in the coil 108.

Various means may be used for adjusting the position of the plate 112, and in the illustrated case, this means consists of an adjustment screw 118 supported by a bracket 120 fixed to the fixed structure of the engine and meshing with teeth formed on an arcuate section 122 of the plate. This construction has the advantage that the adjustment may be made after the ignition system is installed on the engine, without disassembly of any parts, by the use of screwdriver inserted between the rim 20 and the fixed engine structure and brought into working engagement with the head of the screw 118.

Although various embodiments of the invention have been shown by the drawing and described above, it should be understood that the drawing and description are not to be construed as defining or limiting the scope of this invention, the claims which follow being relied upon for that purpose.

What is claimed is:

1. In a breakerless ignition system for a spark ignited engine the combination comprising: a spark gap ignition device, an ignition circuit means connected with said spark gap device and including an electronic switch device for causing the occurrence of a spark at said spark gap device as said switch device is switched from a first state to a second state, a part rotated in synchronism with the operation of said engine, a magnet, a triggering coil coupled with said switching device and operable to switch the latter from said first state to said second state when the voltage across said triggering coil rises to a predetermined level, said magnet being arranged relative to said triggering coil so as to produce a flux circuit passing through said coil, magnetic flux varying means on said rotating part for varying the reluctance of said flux cir cuit through said coil as said part is rotated to thereby induce a varying voltage in said triggering coil, magnetic flux conducting means providing a shunt circuit for magnetic flux produced by said magnet which shunt circuit does not pass through said coil, said magnetic flux conducting means which provide said shunt circuit including at least two parts, and adjustment means for adjustably positioning one of said latter two parts relative to the other to adjustably vary the reluctance of said shunt circuit.

2. The combination defined in claim .1 further characterized by said at least two parts of said shunt circuit forming a flux path including at least one air gap the reluctance of which air gap is varied by adjustably positioning one of said latter two parts relative to the other -by operation of said adjustment means.

3. The combination defined in claim 1 further characterized by said at least two parts of said shunt circuit forming a flux path at least a portion of which is comprised of ferromagnetic material and the cross-sectional area of which flux path at at least one point along said portion thereof is varied by adjustably positioning one of said latter two parts relative to the other by operation of said adjustment means.

4. The combination defined in claim 1 further characterized by said magnetic flux conducting means which provides said shunt circuit including a first ferromagnetic element engageable with one pole of said magnet, a second ferromagnetic element engageable with the opposite pole of said magnet, and a third ferromagnetic element carried by one of said first and second elements and arranged to provide an air gap between it and the other of said first and second elements, and said adjustment means comprising means for adjustably mounting said third element on said one of said first and second elements to permit it to be adjustably positioned relative thereto to vary the size of said air gap.

5. The combination as defined in claim 1 further characterized by said magnetic fiux conducting means which provides said shunt circuit including pole means defining two opposite pole faces for said magnet and a movable ferromagnetic element having a face extending across said two magnetic pole faces, the face of said movable element being so shaped as to have different areas of overlap with at least one of said magnetic pole faces at different positions thereof, and said adjustment means comprising means for adjustably varying the position of said movable element relative to said pole faces.

6 The combination defined in claim 1 wherein said magnet is of an annular shape and is positioned with its axis generally aligned with the axis of said coil, said magnet having opposite magnetic poles on opposite end faces thereof, a ferromagnetic core passing through said coil and positioned so that one end thereof faces said rotating part, connecting means directly magnetically connecting the other end of said core to the adjacent end face of said annular magnet, and said magnetic flux conducting means which provides said shunt circuit and said adjustment means including a ferromagnetic element engaging the other end face of said magnet, and a screw threadably received by said ferromagnetic element and. extending through the center opening of said magnet toward said coil core to provide an air gap between said screw and said coil core the size of which is varied by threadably rotating said screw in one direction or the other relative to said ferromagnetic element.

7. The combination defined in claim 1 wherein said electronic switch device is a silicon controlled rectifier having its gate terminal connected to said triggering coil.

References Cited UNITED STATES PATENTS 2,536,468 1/ 1951 Russell 317-92 3,183,958 5/1965 Davies 317-81 X 3,359,459 12/1967 Smith J. 317-81 VOLODYMYR Y. MAYEWSKY, Primary Examiner US. Cl. X.R. 

